1. Field of the Invention
The present invention is directed to force limiting, energy absorbing couplers for railway vehicles generally and having desired application in mass transit vehicles.
2. Description of Related Art
Overload shear release bolts/bushings are commonly used in mass transit car connectors known as couplers. The purpose behind these shear release bolts/bushings is to limit the maximum load transferred from the coupler to the car frame. Force levels otherwise would exceed this maximum load during a hard coupling or collision with another car. This situation could cause the two cars to sustain crush damage and could lead to passenger injury or death. During an impact, once the bolts/bushings shear and release, the coupler anchor slides back into a pocket in the transit car frame at zero load, absorbing no energy. In a typical application of overload shear release bolts/bushings, four shear release bolts secure a coupler anchor to the frame of a mass transit vehicle, such as a subway car. When there is a compressive force between two cars, the load is shared evenly through all four overload shear release bolts/bushings until a maximum load situation occurs such as during a hard coupling or collision when the bolts/bushings shear and release.
In another design, an energy-absorbing deformation tube is used in series with an overload shear release mechanism, such as the foregoing shear bolt/bushing design which is designed to break at the maximum load the car frame can handle. The deformation tube is set to collapse at a lower load than the foregoing shear bolt/bushing design.
It is generally known in the art to use friction draft riggings in railway vehicles as evidenced by U.S. Pat. No. 3,152,699 (Vickerman); U.S. Pat. No. 2,639,821 (Danielson); U.S. Pat. No. 2,504,253 (Dath); U.S. Pat. No. 2,451,551 (Haseltine); U.S. Pat. No. 2,380,303 (Geiger); and U.S. Pat. No. 2,276,167 (Dalton). Each of these patents incorporates a friction component for shock absorbing purposes. Additionally, U.S. Pat. No. 3,536,314 to Tönne discloses a friction spring for use in a buffer for a railroad vehicle in which frictional engagement between two rings is used to accommodate impact energy. U.S. Pat. No. 2,994,442 to Frederick discloses a kinetic energy absorbing device for a cushioning device in which frictional engagement between slidable shoes converts kinetic energy to heat.